How Maglev Trains Work

Electrodynamic Suspension (EDS)

Above is an image of the guideway for the Yamanashi maglev test line in Japan.

Photos courtesy Railway Technical Research Institute

Japanese engineers have developed a competing version of maglev trains that use an electrodynamic suspension (EDS) system, which is based on the repelling force of magnets. The key difference between Japanese and German maglev train technology is that the Japanese trains use super-cooled, superconducting electromagnets. This kind of electromagnet can conduct electricity even after the power supply has been shut off. In the EMS system, which uses standard electromagnets, the coils only conduct electricity when a power supply is present. By chilling the coils at frigid temperatures, Japan's system saves energy. However, the cryogenic system used to cool the coils can be expensive and add significantly to construction and maintenance costs.

Another difference between the systems is that the Japanese trains levitate nearly 4 inches (10 centimeters) above the guideway. One potential drawback in using the EDS system is that maglev trains must roll on rubber tires until they reach a liftoff speed of about 93 mph (150 kph). Japanese engineers say the wheels are an advantage if a power failure caused a shutdown of the system. Also, passengers with pacemakers would have to be shielded from the magnetic fields generated by the superconducting electromagnets.

The Inductrack is a newer type of EDS that uses permanent room-temperature magnets to produce the magnetic fields instead of powered electromagnets or cooled superconducting magnets. Inductrack uses a power source to accelerate the train only until it begins to levitate. If the power fails, the train can slow down gradually and stop on its auxillary wheels.

The track is actually an array of electrically shorted circuits containing insulated wire. In one design, these circuits are aligned like rungs in a ladder. As the train moves, a magnetic field repels the magnets, causing the train to levitate.

There are currently three Inductrack designs: Inductrack I, Inductrack II, and Inductrack III. Inductrack I is designed for high speeds, while Inductrack II is suited for slow speeds. Inductrack III is specifically designed for very heavy cargo loads moved at slow speeds. Inductrack trains could levitate higher with greater stability. As long as it's moving a few miles per hour, an Inductrack train will levitate nearly an inch (2.54 centimeters) above the track. A greater gap above the track means that the train would not require complex sensing systems to maintain stability.

Permanent magnets had not been used before because scientists thought that they would not create enough levitating force. The Inductrack design bypasses this problem by arranging the magnets in a Halbach array. The magnets are configured so that the intensity of the magnetic field concentrates above the array instead of below it. They are made from a newer material comprising a neodymium-iron-boron alloy, which generates a higher magnetic field. The Inductrack II design incorporates two Halbach arrays to generate a stronger magnetic field at lower speeds.

Notably, the passive magnetic levitation concept is a core feature of proposed hyperloop transportation systems, which is essentially an Inductrack-style train that blasts through a sealed tube that encases the entire track. It's possible that hyperloops may become the approach of choice, in part because they dodge the issue of air resistance in the way the regular maglevs cannot, and thus, should be able to achieve supersonic speeds. Some say that a hyperloop might cost even less than a traditional high-speed rail line.

But whereas maglev trains are already a proven technology with years of operational history, no one has yet built a commercial hyperloop anywhere in the world [source: Davies].